An increasing number of electronic devices are being powered through their USB connectors. For example, many smart phones, MP3 players, tablet computers, etc. may have batteries that can only be charged through their USB connectors. At the USB standard voltage of 5 volts DC, the current available for charging typically ranges from about 500 mA to about 1.5 A. As a result, there is typically a maximum of about 7.5 W available for charging through a USB connector of an electronic device.
The larger the battery of an electronic device the longer it takes to charge. With a maximum available power of 7.5 W, some electronic devices, such as tablet computers, can take many hours to charge. Electronic devices with even larger batteries, such as laptop computers, tend to take an unacceptably long time to charge through a USB port and, as such, are typically provided with an alternative charging port, such as a dedicated charger port.
To reduce charge time, the power available for charging must be increased. Since P=I*V, this can be accomplished by increasing the current, increasing the voltage, or both. However, increasing current increases I2R losses in the cable and connector.
A new standard known as USB Power Delivery (referred to herein as “USBPD”) is in early development by USB Implementers Forum, Inc, the creators of USB technology. For example, a document entitled Universal Serial Bus Power Delivery Specification Revision 1.0, including Errata through 31 Oct. 2012 (Version 1.1), incorporated herein by reference, is available for download from the website at usb.org. Since there is not yet compliance documentation, this proposed standard is years away from implementation, if ever.
A potential drawback of the USBPD specification is that it proposes to provide communication between a host and a device over the power line of the USB bus. This method of communication has several disadvantages including the requirement that a large inductor be added to the circuit to counteract the effect of the large AC bypass capacitor required for signal over power, and because a USB power transceiver must be added to both the host (e.g. power converter) and to the device (e.g. a tablet computer).
Another potential solution for providing higher power to electronic devices is to provide a special, dedicated connector. However, this adds both cost and complexity to the electronic device and its operation.
These and other limitations of the prior art will become apparent to those of skill in the art upon a reading of the following descriptions and a study of the several figures of the drawing.